When you have to talk to someone about a serious, and maybe uncomfortable, topic, it's good to start by saying:

Can I talk to you?

This phrase alerts the listener that you're not just making small talk; you have something serious about. Here are some examples of conversations that you may want to start by saying "Can I talk to you?":

You need to reprimand one of your employees for doing something wrong.

You just got some bad news, and you need to share it with your partner.

You're going to break up with the person you've been dating.

If you want to make this expression a little bit less serious (but still pretty serious), add "for a minute" or "for a second".

To make it more formal, use "May I", "speak with", and "for a moment" instead: